FKBP12 PHYSICALLY AND FUNCTIONALLY INTERACTS WITH ASPARTOKINASE IN SACCHAROMYCES-CEREVISIAE

The peptidyl-prolyl isomerase FKBP12 was originally identified as the intracellular receptor for the immunosuppressive drugs FK506 (tacrolim us) and rapamycin (sirolimus). Although peptidyl-prolyl isomerases hav e been implicated in catalyzing protein folding, the cellular function s of FKBP12 in Saccharomyces cerevisiae and other organisms are largel y unknown. Using the yeast two-h,brid system, we identified aspartokin ase, an enzyme that catalyzes an intermediate step in threonine and me thionine biosynthesis, as an in vivo binding target of FKBP12. Asparto kinase also binds FKBP12 in vitro, and drugs that bind the FKBP12 acti ve site, or mutations in FKBP12 surface and active site residues, disr upt the FKBP12-aspartokinase complex in vivo and in vitro. fpr1 mutant s lacking FKBP12 are viable, are not threonine or methionine auxotroph s, and express wild-type levels of aspartokinase protein and activity; thus, FKBP12 is not essential for aspartokinase activity. The activit y of aspartokinase is regulated by feedback inhibition by product, and genetic analyses reveal that FKBP12 is important for this feedback in hibition, possibly by catalyzing aspartokinase conformational changes in response to product binding.